PLATE E 



I, — A slightly more advanced stage of the condition shown in Plate D, figure i6. 



2. — An early stage in the abortion of a full-grown i-nucleate microspore. X 2,000. 



3. — An early stage of abortion directly following microspore division. X 2,000. 



4. — A full-grown i-nucleate microspore containing very scant light-staining cyto- 

 plasm; from an anther containing i- and 2-nucleate microspores. X 2,000. 



5. — Another type of degeneration of a full-grown I-nucleate microspore. X 2,000. 



6. — An aborted microspore fotmd among i- and 2-nucleate microspores. X 2,000. 



7. — A later stage of the type of degeneration shown in Plate D, figure 13; from 

 an anther containing microspores of the stage of development shown by Plate C, 

 figure 15. X 2,000. 



8. — Degeneration of the generative cell shortly after division. The vegetative 

 nucleus and cytoplasm are still normal. X 2,000. 



9, 10. — Common types of aborted microspores found with mature pollen. Evidently 

 abortion took place before the division of the microspore nucleus. X2,ooo. 



II. — An aborted microspore, of the same type as that shown in figure 7. Found 

 with mattu"e pollen. X 2,000. 



12. — A pollen grain showing abortion of the generative cell and an abnormal vacuo- 

 late condition of the cytoplasm. X 2,000. 



13. — A later stage of the type of degeneration shown in figure 8. The vegetative 

 nucleus and cytoplasm are normal. X 2,000. 



